An ink jet printer of the type frequently referred to as drop-on-demand, has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink is contained in a plurality of channels. Piezoelectric devices or power pulses cause the droplets of ink to be expelled as required, from orifices or nozzles located at the end of the channels. In thermal ink jet printing, the power pulses are usually produced by resistors also known as heaters, each located in a respective one of the channels. The heaters are individually addressable to heat and vaporize the ink in the channels. As a voltage is applied across a selected heater, a vapor bubble grows in that particular channel and ink bulges from the channel nozzle. At that stage, the bubble begins to collapse. The ink within the channel retracts and then separates from the bulging ink thereby forming a droplet moving in a direction away from the channel nozzle and towards the recording medium whereupon hitting the recording medium a spot is formed. The channel is then refilled by capillary action which, in turn, draws ink from a supply container of liquid ink. Operation of a thermal ink jet printer is described in, for example, U.S. Pat. No. 4,849,774.
The ink jet printhead may be incorporated into either a carriage type printer or a page width type printer. The carriage type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead is usually sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage which is reciprocated to print one swath of information (equal to the length of a column of nozzles) at a time on a stationary recording medium, such as paper or a transparency. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath or a portion thereof so that the next printed swath is overlapping or contiguous therewith. The procedure is repeated until the entire page is printed. In contrast, the pagewidth printer includes a stationary printhead having a length sufficient to print across either the entire width or length of the recording medium. The recording medium is continually moved passed the pagewidth printhead in a direction normal to the length of the printhead and at a constant or varying speed during the printing process. A pagewidth ink jet printer is described in U.S. Pat. No. 5,192,959.
It has been recognized that there is a need to maintain the ink ejecting nozzles of an ink jet printhead, for example, by periodically cleaning the orifices when the printhead is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods of time. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to insure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles and also periodically to maintain proper functioning of the orifices. Maintenance and/or priming stations for the printheads of various types of ink jet printers are described in, for example, U.S. Pat. Nos. 4,855,764, 4,853,717 and 4,746,938. Removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059.
It has been found that to properly maintain an ink jet printhead two separate operations must be performed. A conditioning member is typically used to maintain proper condition or operation of the printhead nozzles by priming the nozzles or by vacuuming the face of the printhead to remove any contaminants or ink which may have collected thereon. The second operation is to cap the printhead if the printhead nozzles will be exposed to air for extended periods of time to thereby prevent the ink contained in the nozzles from drying out. To prevent drying, printheads are usually covered with a cap which forms a substantially airtight seal with the face of the printhead. While it is possible to combine the functions of conditioning and capping, it has been found that separate mechanisms for conditioning the printhead front face and for capping the printhead nozzles in a pagewidth printhead are advantageous.
Various methods and apparatus for maintaining the condition of ink jet printheads and for capping ink jet printheads are illustrated and described in the following disclosures which may be relevant to certain aspects of the present invention.
In U.S. Pat. No. 5,206,666 to Watanabe et al., an ink jet recording apparatus having a full-line type recording head rotatably supported between a recording position and a non-recording position is described. A cleaning member contacts the recording head during rotation of the recording head to remove deposited ink or foreign matter. In the non-recording position, the printhead is capped.
U.S. Pat. No. 5,257,044 to Carlotta et al. describes a cap actuation mechanism for use in a maintenance station for an ink jet printhead in a scanning type ink jet printer. A cap located on a cap carriage in an ink jet printer maintenance station provides the functions of printhead nozzle capping, priming, cleaning, refreshing, as well as waste ink management.
U.S. Pat. No. 5,367,326 to Pond et al. describes a pagewidth ink jet printer having a movable cleaning/priming station adapted for movement parallel to and along an array of printhead nozzles. The cleaning and priming station is slidingly moved along a ledge surface so that the cleaning and priming station is maintained a fixed distance from the face of the printhead.
U.S. Pat. No. 5,534,897 filed on Jul. 1, 1993, having the title "Ink Jet Maintenance Subsystem" assigned to Xerox Corporation, discloses an ink jet maintenance subsystem for a full width array thermal ink jet printer. The system includes a translatable maintenance station carriage assembly translating across the width of the full width array printbar and also includes an articulating cap assembly for capping the printbar nozzles when the translatable maintenance station carriage assembly is at a home position outside the edge of the printbar. When the cap assembly moves away from the printbar, a free space area is provided that allows unrestricted translation of the maintenance station carriage assembly.